When installing new bags you must be careful not to puncture the bag, which in my experience is easy to do. A cardboard square with a hole is placed on top of the plastic exhaust pipe. The problem is that you can't see the cardboard square because it's behind the bag. Therefore, when setting up the bag, you should have an idea of the placement. Once you've centered the hole on the outlet, you'll need to slide the piece of cardboard further about 1-1/2 inches to ensure a good seal. At this point, move slowly so as not to tear the bag. If you move fast, the bag will burst.